ATLANTA - A recent study found a possible increased risk of culture-confirmed invasive group A streptococcus (GAS) disease in household contacts of index case patients.
"We were also able to document the risk of probable severe GAS disease requiring hospital care. The risk of subsequent disease was among the immediate family members, and the interval between index case date of culture and household contact date of onset was zero to 26 days, with a mean of 12 days," said Katherine A. Robinson, MPH, at the International Conference on Emerging Infectious Diseases 2000.
"GAS is commonly found in the throat and on the skin. It usually causes mild illnesses like strep throat and impetigo. However, when GAS becomes invasive, it can cause severe illness, including streptococcal toxic shock syndrome and necrotizing fasciitis. The overall incidence of invasive GAS disease is 3.8 cases per 100,000 population, yielding more than 10,000 estimated cases and 1,300 estimated deaths in the United States each year," explained Robinson, who is an epidemiologist in the Respiratory Diseases Branch at the Centers for Disease Control and Prevention (CDC).
In 1995, a working group on the prevention of invasive GAS infection was convened by the CDC. This working group reviewed the criteria for recommending prophylaxis, which included severity of disease, virulence of the strain, increased risk among postcontacts and effective prophylaxis. The working group identified the need for additional data.
"The objective of this study was to determine the subsequent attack rate for both confirmed invasive GAS disease and probable severe GAS disease among household contacts of invasive GAS cases. Index case patients were identified via the Active Bacterial Core Surveillance (ABCs) system/Emerging Infections Program Network between Jan. 1, 1997, and April 30, 1999. Cases were defined as surveillance area residents with a positive isolation of GAS from a normally sterile site or from a wound when accompanied by necrotizing fasciitis," explained Robinson, the ABCs coordinator.
The study population was 12.1 million and included the states of Connecticut and Minnesota and selected counties in California and Oregon. All case patients were telephoned to determine eligibility and to conduct an interview. Eligibility was restricted to household and case patients with community-acquired GAS, and therefore, all household and case patients who lived in institutions or had acquired GAS nosocomially were excluded. Case patients who were homeless, lived alone or did not have a telephone were also excluded.
"We interviewed the case patient or appropriate surrogate for each eligible household to determine any underlying medical conditions of all household contacts and to identify any visits to a physician in the 30 days following the index case date of culture. We extracted medical charts for all contacts who visited physicians to determine type of visit, compliance, test results, antibiotic use and diagnosis. We defined a household contact as one who regularly spent 50% of their nights in a household with the case patient or one who spent 24 or more hours in a household with the case patient in the week prior to the case date of culture," she said.
During the study period, 1,064 invasive GAS cases were reported to the ABCs system. All of these case households were screened to determine eligibility, and, ultimately, 695 were eligible for enrollment in the study. Of the 695 eligible households, 525 (76%) were reachable and agreed to participate.
There were 1,514 household contacts identified and investigated. Fifty-four percent were female, and the age distribution was 0 to 93 years, with a mean of 29 years. Almost 39% were children younger than 18. Approximately 9% of the household contacts reported having at least one underlying medical condition, and 12% reported antibiotic use in the 30-day reference period.
During the reference period, 8.4% (n=127) visited a physician. Of these, 51% had an infectious disease diagnosis. Fifty-six were diagnosed with streptococcal pharyngitis via a positive rapid strep test.
"There were eight cutaneous infections and one X-ray-documented pneumonia with no positive culture. Twenty-four contacts required hospital care in the 30-day period, with 13 hospital admissions and 11 visits to the emergency department (ED). During the study period, we identified one subsequent case of culture-confirmed invasive GAS disease resulting in necrotizing fasciitis," Robinson said.
"In addition, we identified five probable cases with GAS-compatible illness in household contacts including one case of necrotizing fasciitis and four cases with other cutaneous infections. All six of these cases survived, with four admissions to the hospital and two ED visits."
The six GAS case pairs were not evenly distributed in the four surveillance areas. Four of the six case pairs were identified in California, infecting one of every 22 index case households. "This type of geographic information can be a useful indicator for state public health departments in assessing feasibility of prophylaxis," she said.
For more information:
- Robinson KA, Rothrock G, Phan QN, et al. Transmission of invasive group A streptococci within households. Presented at the International Conference on Emerging Infectious Diseases 2000. July 16-19, 2000. Atlanta.
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